1. Field of the Invention
The present invention relates to an interframe adaptive vector quantization encoding apparatus which performs encoding of video signals at high efficiency using vector quantization, and also to a video encoding transmission apparatus which transmits the encoding signals.
2. Description of the Prior Art
First, principle of the vector quantization will be described briefly. The input signal series of K in number are brought together into input vector X={x.sub.1, x.sub.2, . . . x.sub.K }. Then, the K-dimensional Euclidean signal space R.sup.k (X.epsilon.R.sup.k) has the representative points of N in number (i.e., output vector) y.sub.i ={y.sub.i1, y.sub.i2, . . . y.sub.ik }, and set of the representative points is made Y=[y.sub.1, y.sub.2, . . . yHD n]. The vector quantizer determines output vector y.sub.i as hereinafter described from the set of output vectors, and retrieves it. The output vector y.sub.i is in the minimum distance (minimum distortion) to the input vector, and it follows that: EQU if, d(X,y.sub.i )&lt;d (X,y.sub.j ) for all.sub.j X.fwdarw.y.sub.i
wherein, d(X, y.sub.i) represents distance (distortion) between input/output vectors. Then, the input vector X is transmitted or recorded in index i of the output vector. At reproduction, set Y of the output vector y.sub.i can be determined by clustering using the video signal series being the training model (repetition of the selection of the representative points and the quantization of the training model into each representative point until the total distortion becoming minimum). Furthermore, in order to improve efficiency of the vector quantization and versatility of the output vector set, the vector quantization may be performed at separation of the mean value of vectors and the normalization in amplitude.
An interframe adaptive vector quantization apparatus in the prior art will be described.
FIG. 2 is a block diagram of an interframe adaptive vector quantization apparatus in the prior art illustrating a constitution example of an encoding member thereof. In FIG. 2, numeral 1 designates an A/D converter, numeral 2 a raster/block scan conversion circuit where digital video signals in raster form by the A/D conversion are made a block per every m picture elements x n lines (m, n: integer), numeral 3 a vector quantization encoder which encodes the block data at high efficiency by means of vector quantization, numeral 4 a transmission data buffer where the encoded data at high efficiency is stored and transmitted to the transmission path at constant speed, numeral 5 a movement detection control circuit which controls threshold value of movement detection in the vector quantization encoder corresponding to the data amount stored in the transmission data buffer, numeral 6 a vector quantization decoder which decodes the encoded data supplied from the vector quantization encoder and reproduces the block data, numeral 7 a variable delay circuit, and numeral 8 a frame memory.
FIG. 3 is a block diagram of the interframe adaptive vector quantization encoding apparatus in the prior art illustrating a constitution example of a decoding member. In FIG. 3, numeral 9 designates a receiving data buffer where the encoding data supplied from the transmission path is received and stored and then outputted at speed corresponding to the decoding action, numeral 10 a block/raster scan conversion circuit where the block data decoded and reproduced is converted into data in raster form, and numeral 11 a D/A converter.
Encoding and decoding operation of the apparatus will now be described referring to FIG. 2 and FIG. 3.
Input video signals (101) are analog signals which are raster-scanned from the left to the right on the screen and from the upper side to the lower side. The analog signals in raster form are converted into digital signals (102) by the A/D converter 1, and then the digital signals in raster form are made a block per every m picture elements x n lines (m, n: integer) by the raster/block conversion circuit 2, and further vector data S (103) is obtained from the picture element sample within the block.
Difference signal between the vector data S (103) and frame vector data P (104) based on the same position block within the frame memory 8 becomes interframe difference vector .epsilon. (105), which is inputted to the vector quantization encoder 3. The vector quantization encoder 3 applies processing of mean value separation and normalization to the interframe difference vector .epsilon. (105), and performs movement detection using mean value and amplitude coefficient obtained by the processing and using threshold value (106), and performs vector quantization of only vector of significant block based on the movement. And then the vector quantization encoder 3 encodes the significance/insignificance information, the mean value, the amplitude coefficient and the vector quantization index information each using variable length encoding or the like, and outputs the encoding data (107). The transmission data buffer 4 stores the encoding data (107) and transmits it to the transmission path at constant speed according to prescribed transmission speed, and estimates data storage amount (108) and supplies it to the movement detection control circuit 5. The movement detection control circuit 5 controls the threshold value (106) for the movement detection depending on variation of the data storage amount (108).
The encoding data outputted from the vector quantization encoder 3 is encoded according to reverse processing of the encoding in the vector quantization decoder 6, thereby interframe difference reproduction vector .epsilon. (109) is reproduced. The interframe difference reproduction vector .epsilon. (109) obtained in the processing and the frame vector data P (104) delayed by prescribed time by means of the variable delay circuit 7 are added, thereby reproduction vector data S (110) is restored and the block data at corresponding position of the frame memory is updated.
On the other hand, the encoding data (107) after being received and speed-changed in the receiving data buffer 9 is decoded by the vector quantization decoder 6, thereby interframe difference reproduction vector .epsilon. (109) is reproduced. The interframe difference reproduction vector .epsilon. (109) and the frame vector data P (104) passing through the variable delay circuit 7 are added, and reproduction vector data S (110) is restored in similar manner to the processing in the encoding member. The reproduction vector data S (110) is converted into data (111) of raster form by the block/raster scan conversion circuit 10, and the data (111) is converted in D/A conversion by the D/A converter 11 so as to obtain analog reproduction video signal (112).
Next, constitution and operation of the vector quantization encoder and the vector quantization decoder will be described in detail. FIG. 5 shows a constitution example of a vector quantization encoder in the prior art. In FIG. 5, numeral 19 designates a mean value separation and normalization circuit, numeral 13 a movement detection circuit, numeral 23 a distortion operation circuit, numeral 20 a minimum distortion detection circuit, numeral 16 a code book ROM, numeral 17 an address counter, and numeral 18 an index register.
Operation of the vector quantization encoder will be described.
The mean value separation and normalization circuit performs operation as hereinafter described to interframe difference vector .epsilon. (113) being input signal thereof, and converts it into normalization vector x.
Assuming that intrablock mean value of .epsilon.=[.epsilon..sub.1, .epsilon..sub.2, . . . , .epsilon..sub.k ] (k=m.times.n) to be m and amplitude coefficient thereof be .sigma., it follows that: ##EQU1## Approximate expression of .sigma. such that ##EQU2## or the like may be used.
Assuming that EQU xj=(.epsilon.j-m) /.sigma. EQU x=[x.sub.1, x.sub.2, . . . , x.sub.k ]
the mean value m, the amplitude coefficient .sigma., the normalization vector x can be obtained.
The mean value m (114) and the amplitude coefficient .sigma. (118) obtained are inputted to the movement detection circuit 13, and compared with the threshold values T.sub.0, T.sub.1, thereby the significance/insignificance block discrimination, i.e., the movement detection processing is performed according to following conditions and the block discrimination information .nu. (121) is outputted. ##EQU3## The block discrimination information .nu. is transmitted per each block. Only in the case that .nu. is 1, following processing is performed.
The normalization vector x (122) is transmitted to the distortion operation circuit 23 and subjected to following vector quantization processing.
Set of a plurality of output vectors y.sub.i (116) (i=1, 2, . . . , N) is produced using clustering method based on statistical property of the normalization vector x, and written in the code book ROM 16. When the normalization vector x (122) is inputted to the distortion operation circuit 23, the address counter 17 performs count-up in sequence of i=1, 2, . . . , N, and reads the output vector y.sub.i (116) corresponding to the address information i in sequence of y.sub.1, y.sub.2, . . . , y.sub.N from the code book ROM 16 of the output vector. Distortions d (x, y.sub.i) (117) between the normalization vector x and N output vectors y.sub.i read in sequence are calculated sequentially in the distortion operation circuit 23. The distortion calculation is executed according to following formula. ##EQU4## Otherwise, approximate expression such that ##EQU5## may be used.
In the minimum distortion detection circuit 20, the minimum distortion among the N distortions estimated by the above calculation is detected, and the output vector address information i in the code book ROM indicated by the address counter is taken in the index latch 18 and outputted as the output vector index i (120).
The intrablock mean value m (114), the amplitude coefficient (118), the block discrimination information .nu. (121) and the output vector index i (120), all obtained in the above process, are converted into codes being suitable as the vector quantization encoding information (107) and then outputted. In this case, if .nu. is 0, codes in other information are not outputted.
A vector quantization decoder shown in FIG. 4 will now be described.
In FIG. 4, numeral 21 designates an amplitude coefficient multiplier, and numeral 22 a mean value adder.
Among the vector quantization encoding information (107) transmitted from the receiving data buffer 9, the block discrimination information .nu. (121) is first decoded. If .nu.=1, i.e., if the block is significant, the decoded output vector index i (120) is taken in the index register 18. In the code book ROM 16 where the same content as that of the code book ROM of the vector quantization encoder is written, the output vector y.sub.i (119) indicated by the index i (120) is read. The amplitude coefficient .sigma. (118) is multiplied to the output vector y.sub.i in the amplitude coefficient multiplier 21 and the mean value m (114) is added to the product in the mean value adder 22, thereby the interframe difference reproduction vector .epsilon. (109) is decoded. That is, following processing is executed. EQU .epsilon.=[.epsilon..sub.1, .epsilon..sub.2, . . . , .epsilon..sub.k ] EQU .epsilon.j=.sigma..multidot.y.sub.ij +m (j=1, 2, . . . , k)
If .nu.=0, i.e., if the block is insignificant, .epsilon. is decoded and reproduced assuming that m=0, .sigma.=0. EQU .epsilon.=[0, 0, . . . , 0]
Since the interframe adaptive vector quantization encoding apparatus in the prior art is constituted as above described, calculation of .sigma. for normalization and calculation of the square sum (.SIGMA. (a-b).sup.2) in the vector quantization distortion operation must be performed at many times, thereby the circuit scale of the apparatus increases. When these calculations are executed using the approximate expressions, the picture quality may be deteriorated due to the calculation error.
Also in the prior art, it is difficult to obtain a universal output vector set which can cope with the picture image having significantly different statistical properties, such as picture image including a document and drawings as main components, picture image requiring the delicate gradation expression or picture image using different sensor system, thereby content of the code book ROM increases.
Further, there exists the problem of mismatching in the quantization apparatus.
Moreover, in order to establish the synchronization of the video frame between receiving and transmission, time deviation of the top end position between the transmission frame synchronous pattern and the video frame (the number of time slots) must be counted at the transmission side and transmitted to the receiving side, and the top end position of the video frame must be detected from such information at the receiving side and clocks necessary for the decoding processing must be reproduced, thereby the apparatus constitution and the transmission control system become complicated. When the transmission speed is slow, the information amount which can be transmitted in one video frame time becomes small. Even if the speed is smoothed at the buffer memory of the transmission side, the transmission efficiency of the encoding data becomes bad and the synchronization of the video frame between transmission and receiving cannot be established.